2010: iOS 4 also added FaceTime video chat, but only if you had the new iPhone 4.

2011: iOS 5 included iCloud, which let you back up your phone to Apple's servers over the internet. No more syncing with iTunes!

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2011: iOS 5 also added Siri, but it only worked on the new iPhone 4S.

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2012: iOS 6 was one of the most controversial updates. Apple ditched Google Maps in favor of its own homegrown maps app. Apple Maps is still considered inferior to Google Maps.

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2013: iOS 7 was a massive overhaul of the software's design. Apple redesigned all the standard apps that come with your phone.

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2013: Apple showed a preview of iOS 8 in June. It added widgets in the Notification Center and a way to respond to notifications like text messages without exiting the app you're using. It'll be available in the fall.